feat: support multiple Radarr and Sonarr instances

[helitra]

This PR extends SeerrFin’s existing Servarr integration from one Radarr and one Sonarr instance to multiple instances per type, without changing the core request flow.

The goal is not to redesign the plugin, but to let users register additional Radarr/Sonarr endpoints and have the plugin treat them the same way as the current single-instance setup.

What changed

• Added a multi-instance Servarr configuration model.
• Kept legacy single-instance fields for backward compatibility.
• Migrated existing Radarr/Sonarr settings into the new list-based structure automatically.
• Reworked the admin configuration UI to allow adding multiple Radarr and Sonarr instances.
• Added a + flow for creating additional instances.
• Added per-instance defaults and a Radarr-only 4K flag.
• Updated Requests progress handling to resolve the correct instance per request.
• Updated open links in the Requests UI to use the correct Radarr/Sonarr instance.
• Preserved the existing Seerr request flow and quality-profile behavior.

Compatibility notes

• Existing single-instance installs continue to work.
• Legacy Radarr/Sonarr values are still supported and are migrated into the new structure.
• Seerr remains a single instance; only Radarr and Sonarr were expanded.

Testing

Verified locally and in Jellyfin using a separate test manifest and fork release:

• repository added successfully
• plugin installed successfully
• Jellyfin restart and setup successful
• single-instance configs still work
• multiple Radarr/Sonarr instances can be added and saved
• Requests/Progress/Quality Profile data loads correctly
• the correct target instance is used for the request flow

Test release used

• 1.6.5.2
• separate test manifest repo: helitra/SeerrFin-test-manifest
• test manifest URL:
  • https://raw.githubusercontent.com/helitra/SeerrFin-test-manifest/main/manifest.json

[helitra]

[varunaditya-plus]

Thank you for contributing to SeerrFin! A few things you might want to check:

• In createServarrInstanceCard, name, url, key, and default are all applied on load, but Is4k isn’t set through the checkbox, so if a user reloads and saves, it can wipe the state of 4K.
• Sonarr doesn't have a 4K instance toggle like Radarr, but 4K Sonarr is commonly in Seerr setups.
• There is no Seerr serviceId wiring or library/root mapping, so anime vs HD, or any multi-library progress links may pick the wrong instance if TMDB matches more than one.
• Also, it's clear AI has been used to some extent while writing this PR. Could you specify which model(s)/harness(es) were used?